535 FXUS63 KFSD 241530 AFDFSD AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SIOUX FALLS SD 1030 AM CDT FRI MAY 24 2013 .UPDATE... ISSUED AT 1027 AM CDT FRI MAY 24 2013 NO MAJOR CHANGES TO THE FORECAST THIS AFTERNOON. MAY AT SOME POINT IN TIME NEED TO DECREASE POPS BUT WITH SHOWERS DEVELOPING WILL WAIT A LITTLE AND SEE BUT STARTING TO LOOK MUCH MORE SCATTERED IN NATURE SO SOMETHING IN THE 30 TO 50 PERCENT RANGE MAY BE NEEDED. OTHERWISE STUCK OUT A SHORT WIND ADVISORY FOR THIS AFTERNOON IN CENTRAL SOUTH DAKOTA. SHOULD BE A PRETTY LOW END ADVISORY WITH SUSTAINED WINDS OF 25 TO 35 MPH. THE STRONGEST WINDS WILL LIKELY BE IN GREGORY COUNTY. && .SHORT TERM...(TODAY AND TONIGHT) ISSUED AT 412 AM CDT FRI MAY 24 2013 SHARP RIDGING ALOFT CURRENTLY ACROSS THE CWA WILL GRADUALLY LOSE HOLD AS MID LEVEL FEATURE SHIFTS EASTWARD AND IMPINGES A BIT MORE SOUTHWESTERLY FLOW THROUGH THE DAY. KEEWATIN HIGH CONTINUES TO FILTER DRIER AIR AT LOW LEVELS INTO THE AREA ON EASTERLY FLOW... BUT MOISTENING ON STRONG LOW LEVEL JET THROUGH THE WESTERN PLAINS LEADING TO EXPANSION OF LOWER TO MID CLOUDS ACROSS WESTERN SOUTH DAKOTA AND WESTERN AND CENTRAL NEBRASKA GRADUALLY BUILDING EASTWARD. MORE MID LEVEL CLOUDS SHOWING UP OF LATE IN SOUTHWEST NEBRASKA...AND AREA CORRELATES QUITE WELL WITH DEVELOPMENT OF STRONGER ISENTROPIC LIFT. LIFT SPREADS RAPIDLY EAST AND NORTHEAST AND WILL BE ACROSS MUCH OF SOUTHEAST SOUTH DAKOTA BETWEEN 12Z AND 15Z. HOWEVER...LIKELY THE LEADING MID LEVEL SHOWERS WILL DIMINISH LIFTING NORTHEAST WHILE RUNNING INTO DRIER AIR WITH PERHAPS A COUPLE OF SPRINKLES SOMEWHAT AHEAD OF THE MAIN AREA OF PRECIPITATION...EXPECTED TO START TO DEVELOP BY LATER MORNING FROM LOWER BRULE AREAS INTO THE LOWER JAMES VALLEY. MUCH OF TIMING FOR PRECIPITATION DEFINED BY 305K NET ISENTROPIC LIFT...CONSIDERING WHERE DRIER AIR AT LOW LEVELS WILL IMPEDE PROGRESS SOMEWHAT. CONTINUED TO INTRODUCE AN INCREASINGLY BETTER COVERAGE FOR SHOWERS AS LIFT FORCING SPREADS EAST TOWARDS AND EAST OF I29 DURING THE AFTERNOON HOURS. GENERALLY 200-500 J/KG ELEVATED INSTABILITY FROM IN AND AROUND 750 HPA LEVEL INITIATION... SO WHILE THUNDER WILL BE FAR FROM PREVALENT...DOES WARRANT A MORE ISOLATED MENTION. SHOULD ALSO NOTE THAT IT WILL BE QUITE A WINDY DAY ALONG AND WEST OF I29...ESPECIALLY FROM THE JAMES VALLEY WEST. AT THIS TIME...LIKELY WILL BE MARGINAL FOR ISSUANCE OF A WIND ADVISORY...BUT WOULD NOT BE SHOCKED TO TOUCH 30 MPH SUSTAINED OR EVEN GUST TO AROUND 40 MPH AT TIMES. THE SURFACE WINDS WILL GRADUALLY DECREASE THROUGH THE EVENING HOURS AND WILL DROP MORE AFTER MIDNIGHT AS WINDS ALOFT GRADUALLY WEAKEN WITH TIME. THE BAND OF WARM AIR ADVECTION/THETA-E ADVECTION PRECIPITATION IS GRADUALLY EXPECTED TO SHIFT OFF TO THE EAST. NOT MUCH IN THE WAY OF INSTABILITY...AND TOYED WITH THE IDEA OF REDUCING THUNDER MENTION IN THE FORECAST. .LONG TERM...(SATURDAY THROUGH THURSDAY) ISSUED AT 412 AM CDT FRI MAY 24 2013 TOUGH FORECAST THROUGH THE EXTENDED WITH ACTIVE PATTERN AND LITTLE CERTAINTY IN HOW EVERYTHING WILL PLAY OUT. ON SATURDAY...MODEL SOUNDINGS APPEAR TO BE VERY SATURATED ESPECIALLY IN THE LOW LEVELS. MODELS CONTINUE TO WARM THE LOW LEVELS DESPITE THIS...BUT AM CONCERNED IT WOULD TAKE TILL AT LEAST MID DAY IF NOT LONGER TO ERODE STRATUS IN THE LOWEST 1500 FEET. AS SUCH...LOWERED FORECAST HIGHS SOME ESPECIALLY IN THE NORTH AND EAST PORTIONS OF THE FORECAST AREA WHERE STRATUS WILL BE THE MOST STUBBORN. THIS ALSO PLAYS INTO THE AMOUNT OF INSTABILITY. SURFACE BASED CAPE IN SOUTHWEST CORNER OF THE FORECAST AREA CLIMBS TO NEAR 1500 J/KG THROUGHOUT THE DAY...BUT STILL APPEARS TO BE EFFECTIVELY CAPPED AT LEAST FROM THE SURFACE. UNLIKE LAST NIGHT/S MODEL RUNS...MODELS HAVE BACKED OFF SOME ON THE LOW LEVEL JET SATURDAY NIGHT...BRINGING FORCING INTO A QUESTION. AGREE WITH PREVIOUS FORECASTER THAT TALL THIN CAPE PROFILES AND PRECIPITABLE WATER VALUES NEAR 1.30 CREATE GREAT ANTECEDENT CONDITIONS FOR FLASH FLOODING. WITH WEAK MID LEVEL WINDS... PRECIPITABLE WATER VALUES WELL ABOVE THE 95 PERCENTILE AND THE POTENTIAL FOR A NEARLY STATIONARY BOUNDARY...FIELD APPEARS TO BE SET...HOWEVER...ONE THING MISSING APPEARS TO BE A TRIGGER ACROSS THE AREA. CAN/T RULE OUT CONVECTION MOVING INTO THE REGION...BUT AT THIS POINT AM BEGINNING TO QUESTION POPS AND HAVE TRENDED DOWN SLIGHTLY. SIMILAR SET UP SUNDAY WITH LOW LEVEL SATURATION...HOWEVER...APPEARS TO BE MORE SHALLOW AND WITH SLIGHTLY STRONGER WINDS MAY BE ABLE TO MIX OUT STRATUS WITH DAY TIME HEATING. WITH WARM FRONT HANGING ACROSS THE AREA...HAVE A FOCUSING MECHANISM BUT ATMOSPHERE STILL APPEARS TO BE CAPPED AT LEAST FROM THE SURFACE. MODELS REALLY TRY TO ERODE THE CAP BY LATE IN THE DAY AS WAVE APPROACHES FROM THE SOUTHWEST...QUESTION BECOMES WHETHER ELEVATED INVERSION WILL ERODE THAT QUICKLY. STILL APPEARS TO BE A GOOD SET UP FOR FLASH FLOODING WITH PWAT VALUES NEAR 1.3 INCHES...ESPECIALLY FOR ANY STORMS THAT WOULD BE ABLE TO TRAIN IN THE SAME AREA. SHEAR PROFILES DON/T SUPPORT A WIDESPREAD OUTBREAK OF SEVERE WEATHER....BUT MAY BE ABLE TO GET AN ISOLATED STORM OR TWO TO PRODUCE MARGINALLY SEVERE HAIL BASED ON INSTABILITY...ESPECIALLY IF STORMS ARE ABLE TO DEVELOP IN THE NEAR SURFACE LAYER. MUCH OF NEXT WEEK CONTINUES TO REMAIN ACTIVE WITH DIRTY SOUTHWEST FLOW ALOFT AND SHORT WAVE TRAIN MOVING ACROSS THE AREA OVER THE NEXT SEVERAL DAYS AHEAD OF A UPPER LEVEL LOW THAT IS EXPECTED TO IMPACT THE REGION NEXT WEEKEND. MODELS ARE MUCH WEAKER WITH UPPER RIDGING IN THE MID WEEK...AND THEREFORE...KEPT MEDIUM RANGE POPS THROUGH THE EXTENDED WITH THE CHANCE OF THUNDERSTORMS. && .AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING) ISSUED AT 645 AM CDT FRI MAY 24 2013 KHON ON EDGE OF STRONGER GRADIENT ALOFT THIS MORNING...AND WILL KEEP A COUPLE HOURS OF NON CONVECTIVE LOW LEVEL WIND SHEAR TO START THE MORNING BEFORE THE WIND PROFILE STARTS TO MIX OUT. OTHERWISE...MASS OF LOWER TO MID LEVEL CLOUDS DEVELOPING IN WARM AIR ADVECTION ZONE THROUGH MUCH OF NEBRASKA AND SOUTH DAKOTA. AS A WEAK WAVE SLIDES UP THROUGH THE WESTERN PLAINS...THIS WILL HELP TO IGNITE SHOWERS AND A FEW THUNDERSTORMS IN FOCUSED WARM AIR ADVECTION ZONE PUSHING ACROSS THE AREA TODAY. ALL INDICATIONS ARE THAT LIFT FORCING WILL BECOME MORE FOCUSED AS AREA SHIFTS TO NEAR AND EAST OF INTERSTATE 29 BY AFTERNOON. WITH INSTABILITY PROFILES FAIRLY NARROW...PREFER TO KEEP OVERALL THUNDER MENTION WITH BAND MINIMAL. FAVORABLE SET UP FOR DEVELOPING STRATUS FIELD BEHIND PRECIPITATION OVERNIGHT TONIGHT...AND LIKELY TO GET INTO LOWER MVFR TO UPPER IFR CEILINGS ALONG WITH SOME MVFR VISIBILITIES. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...WIND ADVISORY UNTIL 7 PM CDT THIS EVENING FOR SDZ050-052-057-058- 063-064. MN...NONE. IA...NONE. NE...NONE. && $$ UPDATE...08 SHORT TERM...CHAPMAN LONG TERM... AVIATION...CHAPMAN